The invention relates to a wheel suspension for steered wheels of motor vehicles. The suspension system of the invention is connected to the wheel carrier by first and second lower suspension arms connected to converge toward the wheel carrier from spaced positions on the vehicle body. A shock absorber and spring are arranged between the body and the wheel suspension wherein the spring is supported on at least one of the suspension arms to produce a transverse component of force through the intersection of the spring strut and the arm to which it is attached. The features of the system are such that this force is multiplied by a lever arm between the point of articulation of suspension arm at the wheel carrier and the idealized steering axis formed by the extension of the suspension arms. The proportionate transverse element of force assumes a lower value for a steering angle on the inside curve than for a steering angle on the outside of the curve.
In this connection, a transverse link having a point of articulation on the wheel carrier, a telescopic shock absorber designed as an integral part of the wheel carrier, or, equally, a combination of two individual suspension arms can serve as upper wheel suspension element. The advantage of individual suspension arms of this type lies particularly in the definition of an ideal steering axis, which can, if necessary, be realized independently of design constraints.
In attempting to ensure a kinematic behavior of the wheel suspension that is as favorable as possible, the designer may consider the wheel camber, the caster, spring action and the damping and roll behavior, and the steering return as only a few of the parameters. To create a reliable wheel suspension of simple design, the designer is mostly forced into compromises. With regard to driven wheels of the wheel suspension the steering return can be especially problematical in this connection because of drive effects and of the free play of the cardan shafts (drive shafts).
It is an object of the invention to create a wheel suspension having the features discussed above, without extra constructional expenses and without the impairment of other axial kinematic parameters, to ensure a reliable steering return and an improved free play of the cardan shafts for driven wheels.
In accordance with the invention, it is proposed to support the suspension springs at one of the lower suspension arms in such a way that the spring exerts a transverse component of force which sets a steering angle. In the straight-ahead driving position of the wheels, this transverse component of force is compensated by the steering assembly via the transverse component of force at the opposite wheel suspension. Because of the geometrical design of the suspension arm, however, when a bend is being taken the transverse component of force or the resultant aligning torque at the wheel on the outside of the bend is greater than the oppositely directed torque on the wheel at the inside of the bend, so that a resultant aligning torque is exerted on the wheels or the steering assembly. The spring utilized for this purpose preferably can be a helical compression spring or a pneumatic spring.
The more specific design features which enhance the ability to achieve the above objectives include the location of various articulation points with regard to the wheel carrier and other elements of the vehicle. Specifically, the lower end of the spring is connected to the first arm at a position between the articulation point with the wheel and its articulating point with the body. The upper end of the spring strut is connected between the articulation points for the lower suspension elements where they are connected to the body and preferably adjacent to the straight line connecting these points. The spring is aligned substantially parallel to the axis of rotation for the wheel when the vehicle is in a straight-ahead driving position. A line of symmetry is defined between the first and second suspension arms which is inclined toward to the rear of the vehicle at an angle of about 15.degree.. Similarly, the straight line connecting points of articulation of the suspension arms on the side of the wheel carrier forms an obtuse angle with this line of symmetry. A connecting straight line of the points of articulation for the suspension arms with the vehicle body is inclined inwards in the driving direction at about 15.degree. to the longitudinal axis of the vehicle. Furthermore, the first suspension arm is arranged to be inclined upwards and backwards at an angle in relation to the transverse plane through the vehicle or to the wheel axis. The spring strut is formed from a telescopic shock absorber and a spring which grips the suspension arm.
This design is particularly favorable for the spring, especially a spring strut composed of telescopic shock absorber and spring, to grip at the forward suspension arm, and for the support of the spring strut on the body side to lie between the suspension arms. The supporting points of the spring strut or the straight line connecting them can be aligned approximately transverse to the longitudinal axis of the vehicle or parallel to the wheel axis in the straight-ahead driving position, whereby the transverse component of force at the suspension arm assumes a favorable value.
Other features produce a further improvement in the steering return and, for driven wheels, in the free play between spring strut and cardan shaft.
Firstly, because of the arrangement of the suspension arms that has been described, there is a favorable influence on the measure "a" which defines the lever arm of the disturbing force in the region of the wheel axis. The measure "a" is therefore the distance between the steering axis and the vertical plane through the center of the wheel at the level of the wheel axis. If the measure "a" is designed so that it takes the value 0 or nearly 0 in the straight-ahead driving position of the vehicle wheels, then because of the features according to the invention the result is that the measure "a" is smaller for a lock on the outside than on the inside of the bend. For driven wheels and a corresponding drive torque during acceleration), this causes an aligning torque at the steering assembly, which results from the propelling forces.
It is further achieved by this suspension arm arrangement that when a lock is applied to the wheel the front suspension arm and the cardan shaft are always deflected in the same direction (forwards or backwards in the plan view). Since the spring or the spring strut is supported at this suspension arm, the lower section of the spring is moved correspondingly at the same time. In this way, the separation between spring or spring strut and cardan shaft remains essentially the same in the straight-ahead driving position and when a wheel lock is applied, so that no problems arise concerning the free play.